Classical approaches to the study of airline competition involve either assessing market concentration or studying rivalry dynamics, through adaptive responses to competition. However, these methods often lack precision at the individual level or reach the limits of computational complexity. To leverage the advantages of both methods, we discuss various measures of competitive intensity between two airlines using bivariate statistical analysis, based on their flight supply strategies across European routes. First, four pairwise symmetric indices are presented and compared. The weighted Jaccard index is identified as the best measure and used to examine the European domestic market in the first and third quarters of 2023. The results show the consistency of the index with real competitive situations. In addition, an asymmetric version of the weighted Jaccard index is introduced for further research and discussion.